[SOLVED] Ask about an error in matplotlib streamplot "The rows of 'x' must be equal"

Ask about an error in matplotlib streamplot "The rows of 'x' must be equal"

I'm trying to plot (B_x,B_z) field line an the code is written below. The function I used is 'streamplot(x,z,Bx,Bz)'. After the running, 'x','z','Bx',and 'Bz' have a type as a float64 and the size were (30L,30L), equal.

However, orange canvas plot of the range (0,1) and "ValueError: The rows of 'x' must be equal" are shown after the running. What is the problem in the code?

import numpy as np
import math as m
from matplotlib.pyplot import cm # color map
import matplotlib.pyplot as plt

r_E=6.4*10**6 # (m)
B0=0.0001

Earth = plt.Circle((0, 0), 6400000,color='orange')

plot=plt.figure()
x,z=np.mgrid[-9000000:9000000:30j, -9000000:9000000:30j]
r=np.sqrt(np.add(np.square(x),np.square(z)))
ax=plot.gca()
ax.add_patch(Earth)

B_x=[]
B_z=[]
for i in range(len(x)):
    bx=[]
    bz=[]
    for j in range(len(x)):
        bx.append(B0*(r_E/r[i,j])**3*(x[i,j]*z[i,j]/r[i,j]**2)*(1-( 3+x[i,j]/(x[i,j]**2)**(1.0/2) )/8))
        bz.append(B0*(r_E/r[i,j])**3/r[i,j]**2*(z[i,j]**2-(x[i,j]**2)*(3+x[i,j]/(x[i,j]**2)**(1.0/2))/8))
    B_x.append(bx)
    B_z.append(bz)

Bx=np.asarray(B_x)
Bz=np.asarray(B_z)

ax.streamplot(x,z,Bx,Bz)
plt.show(plot)

Solution

streamplot needs x and z to be vectors. Try:

x = np.linspace(-90000000,9000000, 30)
z = np.linspace(-90000000,9000000, 30)
ax.streamplot(x,z,Bx,Bz)